The CD43 molecule, also called sialophorin or leukosialin, is a cell-surface molecules expressed on most of hematopoietic cells except erythrocytes. Human CD43 has a mucin-like extracellular domain of 235 amino acids (aa), a transmembrane domain of 23 as and a 123 as intracytoplasmic domain, all encoded by one exon (Pallant et al., Proc Natl Acad Sci USA. 1989, 86:1328-32; Shelley et al., Proc Natl Acad Sci USA 1989, 86:2819-23). The extracellular domain of human CD43 is rich the amino acids serine (46 residues) and threonine (47 residues), most of which carries about 80 0-linked carbohydrate chains. In addition, CD43 carries 1 N-linked carbohydrate chain. The structure of these 0-glycans varies from one cell type to another (Carlsson et al., J Biol Chem. 1986, 261:12787-95).
The CD43 gene consists of two exons, separated by a 378 by intron, whereby the entire translation product is encode by the second exon (Shelley et al., Biochem J. 1990, 270:569-76). CD43 has been believed to be a specific leukocyte-type marker restricted to most of leukocytes, platelets and hematopoietic stem cells, except for erythrocytes (Remold-O'Donnell et al., Blood. 1987, 70:104-9; Fukuda, Glycobiology. 1991, 1:347-56). However, the expression of CD43 in human tumor cells of non-hematopoietic origin, such as a human uterine cervix cancer cell line (CaSKI), a human lung cancer cell line (A549), a human breast adenocarcinoma cell line (MCF7), a human fibrosarcoma cell line (HT 1080), and human colonic adenocarcinoma cell lines (COLO 205, HT 29, Caco-2, DLD-1 and SW480), has been demonstrated (Fernandez-Rodriguez et al., Tumour Biol. 2002, 23:193-201). CD43 is also expressed in human colon cancer tissue (Sikut et al, Int J. Cancer. 1999, 82:52-8; Jung et al, Korean J Pathol. 38:8-14).
Biosynthetic studies show that the CD43 precursor, with a predicted size of around 40 kDa (including one N-glycan), migrates with an apparent molecular mass of 54 kDa upon electrophoresis. This precursor is subsequently converted to a mature glycosylated molecule with sized from 115 kDa to up to more than 200 kDa due to variable glycosylation. Thymocytes, CD4+T lymphocytes and monocytes express more of a 115 kDa isoform, whereas a 130 kDa form is found mostly on activated CD4+T cells, CD8′ resting and activated T cells, neutrophils, platelets and B cells (Rosenstein et al., Immunol Res. 1999, 20:89-99). It seems that more than one isoform can be co-expressed on the surface of the same cc 11. A tightly regulated post-translational 0 glycosylation pattern results in these characteristic molecular weight isoforms that are differentially expressed in different cell types. Especially, expression of core 2β-1, 6-N-acetylglucosaminyltransferase (C2GnT) results in expression of the 130 kDa CD43 isoform in thymocytes and T cells (Piller et al., J Biol. Chem. 1988, 263:15146-50).
Until recently, more than 17 anti-human CD43 antibodies had been reported. Most of these antibodies react with carbohydrate epitopes on the extracellular domain and all known anti-CD43 antibodies detect the CD43 protein expressed on mature hematopoietic cells (Table 1). Thus, they are not efficient at detecting or eradicating leukemic or lymphoma cells.
TABLE 1Anti-CD4antibodyCD43-positve cellsCD43-negative cellsEpitope*ReferenceT305Activated CD4+ T cells,Granulocytes,Core-21, 2CD8+ T cells,erythrocytes, plateletsthymocytes, myeloidcarbohydrateprecursors in bonemarrowL10T cells, thymocytes, BErythrocytes1-78 Sialidase-3cell lines, monocytes,resistantneutrophils, platelets1-78L2T cells, thymocytes, BErythrocytescell lines, monocytes,neutrophils, platelets84-3C1Bone marrow cells,Platelets, erythrocytesSialidase-sensitive4thymocytes, T cells,carbohydratemonocytes,granulocytesMEM-59Most of leukocytes,Neuraminidase-5, 6CD34+ bone marrowsensitivecellscarbohydrateMT-1, L60T cells, monocytesB cellsNeuraminidase-7DFT1T cells, monocytesB cellssensitivecarbohydrate1G10T cells, NK cells,B cells, Erythrocytes8granulocytesCBF.78T cells, subsets ofNeuraminidase-9monocytes andresistantgranulocytesRDF/AD-9,T cells, monocytes,B cellsNeuraminidase-granulocytessensitivecarbohydrate161-46T cells, monocytes,B cellsNeuraminidase-granulocytesresistant4D2COLO 205, K562,intracellular10 Jurkat(337-343)4D1Activated CD4+ T cells,B cellsCore-2Mukasa etmonocytescarbohydrateal., 1999*1. Fox et al., J Immunol. 1983, 131: 762-7;2 Saitoh et al., Blood. 1991, 77: 1491-9;3 Remold-O'Donnell et al., Blood. 1987, 70: 104-9;4 Borche et al., Eur Jlmmunol. 1987, 17: 1523-6;5 Stefanova et al., Folia Biol (Praha). 1988, 34: 255-65;6 Alvarado et al., Eur J Immunol. 1995, 25: 1051-5;7 Stross et al, J Clin Pathol. 1989, 42: 953-61;8 Horejsi et al., 1997, In Kishimoto T, et at, Leucocyte Typing, Vol. VI: White Cell Differentiation Antigens 494. Garland, New York and London;9 Tkaczuk et al., Tissue Antigens. 1999, 54:1-15;10 Sikut et al., Int J Cancer. 1999, 82: 52-8;11 Mukasa et al, Int Immunol. 1999, 11: 259-68.